Balancing machines are used for balancing rotors. In this process, the mass distribution of a rotor in relation to the axis of rotation thereof is measured and is improved by adding or removing compensating masses until the forces and vibrations caused by the unbalance lie within acceptable limits. Some components of the mass distribution, for example the unbalance of moments, can only be determined during rotation. For this reason, a balancing machine comprises a rotatable bearing and a drive for the rotor as well as measurement means. To determine unbalance, the rotor is set in rotation, and as a result the forces due to unbalance generate vibrations which can be measured by a vibration sensor. The size and position of compensating masses are calculated from the measured values.
Errors in the measurement process, damage to the rotor and malfunctions of the balancing machine can lead to the calculation of incorrect compensating masses, in such a way that after the balancing process the rotor has an excessive residual unbalance. In more comprehensive production processes which include a balancing process, errors of this type may lead to serious failures and this may result in losses due to broken parts. There is therefore a great need to identify errors which occur during balancing using balancing machines as early as possible and largely to prevent interruptions and damage due to errors.
It is known to carry out automatic monitoring of balancing machines by randomly checking the balancing results. Various directly measurable values, such as driving power or vibration displacement, are checked individually to see whether they exceed limits. Furthermore, active safety measures protect against operating errors, for example by automatically switching off the drive when a predetermined rotational speed limit is exceeded. In general, detailed error identification is left to the specialist staff. In this case, the progression of the measurement results over time is generally analysed on the basis of a long measurement. Signal spectra and time frequency representations of the measurement results are also tested.
EP 2 034 284 A2 discloses a method for the detection and diagnosis of errors in a balancing machine, in which it is assumed that the process of the dynamic behaviour of the machine can be modelled as a linear, error-free system, an overdetermined set of linear equations being formed which contain input and output data of the process and unknown states of the assumed linear system, the number of states required to describe the dynamic behaviour being extracted using mathematical calculations such as orthogonal or diagonal projection to form a matrix of the same rank as the assumed linear system, and singular values being calculated using singular value decomposition to obtain an approximate feature for the order of the assumed linear system. This known process-model-based method is used to detect loose connections in the region of the sensor fixing or in the region of the base fixing.
DE 199 38 722 A1 further discloses a method for analysing rolling bearings built into machines, in which a signal generated by the rolling movement is captured by a sensor and the amplitude of the signal is evaluated to detect the presence of damage to a rolling bearing running surface. This takes into account a dynamic model of the rolling bearing in the machine, and this model takes into account at least the contact rigidity of the rolling bearing, on both sides, to calculate, for signal amplitude evaluation, the transfer function between a force caused by the damage and the corresponding sensor signal.
DE 199 07 454 A1 further discloses a method for model-based vibration diagnosis monitoring of rotating machines, which is intended to determine more precisely the links between the vibration properties of the machine and operating parameters. In this case, the monitoring and analysis are carried out in the operating phase, and the dynamics of the operating parameters are removed from the monitoring so as to differentiate between limits being exceeded because of fluctuations in the operating parameters and limits being exceeded because of actual state changes of the machine.